1. Field of the Invention
The present invention relates to a bacterial cellulose film, and in particular relates to a bacterial cellulose film with a density gradient in the direction of the film thickness.
2. Description of the Related Art
Bacterial cellulose (BC), also named microbial cellulose, refers to cellulose produced by microorganisms. Bacterial cellulose is formed by a linkage of β-1,4 glucosidic bonds between carbon atoms and shows properties of high purity and water content, and excellent ductility and mechanical strength. The strain for producing bacterial cellulose includes Acetobacter xylinum. The obtained cellulose generally forms fibers which constitute a non-woven film in a reticular structure on the surface of a culture medium. The fiber in general has a diameter of approximately 2˜100 nm, which is about 1/100th fiber diameter of the plant. However, the fiber of bacterial cellulose has a chemical structure identical to the plant fiber. Because of the unique physical properties, bacterial cellulose is applicable in several fields, such as biomedical materials (EP 1,438,975, EP 0,396,344 or WO 01-61026), electronic materials (US 2008/220333), acoustics (EP 0,457,474, U.S. Pat. No. 5,274,199 or JP 6-284495) and special papers and cosmetics (JP 10-077302, JP9-838803 or FR 2,924,342) etc.
In the field of biomedicine, the bacterial cellulose film has been considered one of the best substitutes for skin, providing effects of alleviating pain, absorbing secretions from wounds, providing wounds with water and enhancing and improving the wound recovery. The bacterial cellulose film also shows excellent biocompatibility and biosafety.
Johnson and Johnson Product Inc. has provided a dressing for burn wounds by using bacterial cellulose films with or without medicines (U.S. Pat. No. 4,588,400). WO 86/02095 discloses a method for producing a bacterial cellulose film with a thickness of about 0.2˜3 mm by culturing A. xylinum in a medium containing Tea Sinesis as nitrogen sources and glucose as carbohydrate sources under 26˜96 hours of stirring at a temperature of 28° C. A film produced by the method has been sold as a trademark BIOFILL® for treatment of skin injuries like artificial skin substitutes.
The Xylos Corporation filed several patent applications for bacterial cellulose films. For example, US 2005/0019380A1 provides a use for bacterial cellulose film to treat chronic wounds. WO2005/018435A2 and US2007/0286884A1 discloses an implantable microbial cellulose material for hard tissue repair and regeneration. EP1849463A2 provides a microbial cellulose material for use in transdermal drug delivery systems.
L'oreal Sociétié Anonyne, FR, has also filed several patent applications relating to microbial cellulose. For example, FR 2924340 discloses a use of fingers maintenance and cosmetics. FR2924342 provides a use for lip care and cosmetics. JP2009-051829 discloses a combination of microbial cellulose films and cosmetic powders. FR2916948 discloses a long-lasting perfume primarily constituted of microbial cellulose films. FR2916971 provides a microbial cellulose paste for puffy eyes.
Regarding the unique physical property, the bacterial cellulose film has been prospected for broad uses. Study for new applications and novel properties of the bacterial cellulose film are already flourishing in the field.